Month: June 2023

Gas Compressibility Factor Correction for Nonhydrocarbon Gases

Wichert and Aziz (1972) have presented a correlation that allows the use of the Standing-Katz graph (Figure 4-1) in the presence of nonhydrocarbon gases. In this case corrected pseudocritical values are and where the term ε3 is a function of the H2S and CO2 concentrations given by that can also be obtained graphically from Figure 4-3. Figure 4-3. Pseudocritical… Continue reading Gas Compressibility Factor Correction for Nonhydrocarbon Gases

Pseudocritical Properties from Gas Gravity

In the absence of detailed composition of a natural gas, Figure 4-2 can be used to relate the gas gravity (to air) with the pseudocritical properties of gas mixtures. Using the results of Example 4-2, the calculated molecular weight is 18.92, leading to γg = 18.92/28.97 = 0.65. From Figure 4-2, ppc = 670 psi and Tpc = 375°R, which compare with 671 psi and… Continue reading Pseudocritical Properties from Gas Gravity

Real Gas Law

The behavior of natural gas mixtures can be approximated by the real gas law where Z is the compressibility factor, also called the gas deviation factor in the petroleum engineering literature. The universal gas constant, R, is equal to 10.73 psi ft3/lb-mol-°R. Equation (4-2) is a general equation of state for gases. The gas compressibility factor for mixtures of… Continue reading Real Gas Law

Gas Gravity

Gas gravity, as used in natural gas production and reservoir engineering, is the ratio of the molecular weight of a natural gas mixture to that of air, itself a mixture of gases. Gas gravity is perhaps the most important defining property of a natural gas because almost all properties and, in fact, the actual description… Continue reading Gas Gravity

Introduction

Natural gas reservoirs produce hydrocarbons that exist primarily in the gaseous phase at reservoir conditions. To predict the gas production rate from these reservoirs, there is a need to review some of the fundamental properties of hydrocarbon gases. This is particularly important (more so than in the case of oil reservoirs) because certain physical properties… Continue reading Introduction

Fetkovich’s Approximation

Vogel’s correlation, normalizing qo by qo,max, is frequently not in close accordance with field data. Fetkovich (1973) suggested a normalization with , and in a flow equation of the form the relationship becomes Equation (3-63) requires the determination of two unknowns, the absolute open flow potential, qo,max, and the exponent n. Both of them are characteristic of a specific well and… Continue reading Fetkovich’s Approximation

Generalized Vogel Inflow Performance

If the reservoir pressure is above the bubble point and yet the flowing bottomhole pressure is below, a generalized inflow performance can be written. The following approach enables generation of an IPR that has a straight portion for pwf ≥ pb, and follows the Vogel equation for pwf < pb adapted to the straightforward logic found in Standing (1971). This can be… Continue reading Generalized Vogel Inflow Performance

Oil Inflow Performance for a Two-Phase Reservoir

Vogel (1968) introduced an empirical relationship for qo based on a number of history-matching simulations. The relationship, normalized for the absolute open flow potential, qo,max is where, for pseudosteady state, where ko is the effective permeability to oil that might be estimated from a pressure buildup test. Therefore, The convenience of the Vogel correlation is that it allows the use of… Continue reading Oil Inflow Performance for a Two-Phase Reservoir